1. Technical Field
This invention relates to energy absorption apparatus for preventing a vehicle from unrestricted impacting of a stationary roadside structure. More specifically, this invention relates to the de-acceleration of a vehicle by an energy absorbing device before it reaches a stationary structure. Such energy absorbing apparatus include impact attenuation barriers and support elements for roadway signs and the like. Support elements of this nature are characterized by break-away posts having approved shear impact characteristics that meet the vehicle de-acceleration requirements upon impact as having certain engineering design requirements as per The American Association of State Highway and Transportation Officials (AASHTO) and the FHWA""s Manual of Uniform Traffic Control Devices (MUTCD) and other design codes"" requirement.
In addition, in evaluating impact attenuation systems, certain tests performance levels have been established by the federal government including the NCHRP 350 test 1, 2 and 3. Each of these test requirements of performance of vehicles impacting attenuation barrier include independent and interdependent crash performance perimeters with the primary performance characteristic requirement of an acceptable de-acceleration rate of the crash vehicle. Support elements for a roadway sign are evaluated for their break-away characteristics having been tested and approved so as to meet maximum de-acceleration rates of a vehicle upon such impact.
2. Description of Prior Art
A number of prior art devices are directed towards the problem of energy absorption of a vehicle impact with a stationary structure such as bridge abutments, parapets, traffic elements and rigid guard rails. Many of such devices provide a collapsible structure of inner engaging deformable elements such as overlying guardrail sections, honeycomb structures and crushable enclosures filled with energy absorption material.
All of such devices must meet government performance standards as in the National Cooperation Highway Research Program, NCHRP, Department 350 by the National Research Commission. These standards are directed towards the safety performance evaluation of highway features for longitudinal barriers, terminals and crash cushions, support structures, work zone traffic, central devices and utility poles.
A variety of impact attenuation systems have been developed, see for example U.S. Pat. Nos. 3,845,936, 5,660,496, 5,112,028 and 5,011,326. All of the above prior art patents rely on the energy absorption properties of material deformation and energy absorption and elaborate structural configurations placed in front of stationary barriers to be protected.
The present invention is directed towards energy absorption devices that dissipate impact forces of a vehicle before it reaches a roadway object by use of multiple break-away posts elements. Such post elements meets FHWA approval for break-away characteristics which include an acceptable meters per second de-acceleration rate of the vehicle as it impacts energy absorption device. The plurality of such posts elements are arranged to sequentially engage the vehicle wherein each posts incrementally de-accelerates the vehicle at a known rate from the initial post impact to the final vehicle resting point. Preferably the apparatus of the invention includes multiple posts extending from a central mounting base which is in turn buried in the foreground of the structure to be protected.